Behavior maintained and controlled by scheduled injections of drugs in nonhuman primates serves as an experimental model of drug seeking behavior in man. The purpose of the present project is to investigate the acquisition and maintenance of orderly sequences of behavior leading to injections of narcotic analgesics (e.g. morphine), barbiturates, or psychomotor stimulants (e.g., cocaine and d-amphetamine). Behavioral sequences will be controlled by second-order schedules in which drug injections occur only after completion of several consecutive schedule components; each schedule component terminates with the brief presentation of a stimulus that has been associated with drug injection. This procedure permits the dissociation of the drug seeking behavior from the direct pharmacological effects of the drug. In one series of experiments, the conditioned reinforcing effects of the stimulus associated with injection will be studied in the rhesus monkey and the chimpanzee. Characteristics of performances will be compared under formally comparable second-order schedules of food presentation and drug injection. In a second series of experiments, a range of schedule parameter values using fixed-interval and fixed-ratio schedule components, and a range of drug dosages will be studied in the squirrel monkey and the rhesus monkey. A third series of experiments, using selected schedule parameters and drug dosages, will be concerned with the effects of pretreatment with various classes of drugs (e.g. nalorphine, naloxone, cyclazocine, methadone, chlorpromazine, chlordiazepoxide). The overall objective of this research will be to specify behavioral and pharmacological variables, past and present, which determine how drugs control behavior.